Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$38.47	3.838%	$39.9465	$39.95	$39.95	$39.90
Purchase #2	$134.49	4.266%	$140.2273	$140.23	$140.25	$140.20
Purchase #3	$28.26	8.225%	$30.5844	$30.58	$30.60	$30.60
Purchase #4	$99.44	3.808%	$103.2267	$103.23	$103.25	$103.20
Purchase #5	$33.40	11.432%	$37.2183	$37.22	$37.20	$37.20
Purchase #6	$205.62	9.874%	$225.9229	$225.92	$225.90	$225.90
Purchase #7	$42.46	6.802%	$45.3481	$45.35	$45.35	$45.30
7 purchase totals =	$582.14		$622.4742	$622.48	$622.50	$622.30